1. Field of the Invention
The present invention relates to uninterruptible power systems. More particularly, the present invention relates to no-break power supplies that keep an external load electrically isolated from the power supply while assuring adequate power to the external load. The present invention also relates to standby power systems for supplying power to an external load in the event of an interruption or change of power provided by the source of power.
2. Description of Related an Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
It is customary in situations of critical electrical power requirements to provide an auxiliary power source which can be switched to and from the load in the event of commercial power failure or excessive power variations. In some situations, however, the criticality of the load is such that interruptions or variations in power caused by such switching, although slight, cannot be tolerated. For example, during the countdown period prior to launch of a space vehicle, it is very important that the power supplying the load to the various computers and data equipment be uninterrupted. Typically, computer systems require a constant power supply. Interruptions in the power supply can erase memory and injure the software and hardware of the computer. Other situations where uninterruptible power supplies are considered important include: automatic banking services, automatic industrial processes, communication and signaling centers for maritime and aerial transportation, radio and television stations, and various emergency and security services.
Commercial power alone is generally not considered sufficiently reliable as a sole source of power for such usages. Interruptions commonly occur and loads may vary as other users come on and off the commercial power line. These problems are enhanced in the lesser developed countries where power systems are only in the initial stage of development.
Uninterruptible power systems are generally known within the prior art. Such uninterruptible power supplies usually comprise a generator and two prime movers, one of which normally drives the generator, and the other normally being stationary. When the normally operating prime mover ceases to function for any reason, the normally stationary prime mover is brought up to speed and is connected to drive the generator, usually through a clutch, thereby insuring a continuous supply of current from the generator. Commonly, a kinetic energy supply and device such as a flywheel or a D.C. dynamoelectric machine is coupled to the generator and supplies energy thereto during the transitional period when the generator load is being transferred from one prime mover to the other. One prior art type of no-break power supply comprises an internal combustion engine adapted to be connected through a normally disengaged clutch to a flywheel, the flywheel being connected in turn to the rotor of an electric generator which in turn is connected to the rotor of an A.C. motor. Another prior art type of no-break power supply employs a D.C. dynamoelectric machine in place of the flywheel, both of these devices acting to supply kinetic energy during the aforementioned transitional period.
In the operation of a prior art no-break power supply of either of the aforementioned types, the generator and kinetic energy supplying device are normally driven by the A.C. motor. When there is a failure of the A.C. motor, as, for example, may be caused by an interruption in the power supplied to the A.C. motor, the internal combustion engine is started automatically, brought up to speed, and the clutch is then engaged. The internal combustion engine then drives the generator. During the transitional period when the load is being shifted from one prime mover to the other, the kinetic energy of the flywheel or D.C. machine is utilized to maintain the rotation of the generator.
The prior art shows the number of patented devices that supply uninterruptible power to an external load. U.S. Pat. No. 2,688,704 describes a motor-generator-engine assemblage arranged so as to provide a constant source of electrical power. This device employs a clutch as the switching arrangement. U.S. Pat. No. 3,221,172 is a no-break power supply employing a differential between the primary motor and the standby motor. U.S. Pat. No. 3,305,762 discloses an improved method for maintaining the supply of electrical energy to a load during an interruption of the normal supply of electrical power. This device employs a clutch of the eddy current type. U.S. Pat. No. 3,458,710 is an emergency power system providing an uninterrupted power source having an electric generator for supplying energy to a load, a first motor adapted to be connected to a source of power external as a power system, and a second motor for driving the generator. This system also provides an auxiliary generator driven by a diesel engine for supplying the second motor through a relay connection. Finally, U.S. Pat. No. 3,810,116 relates to systems for capturing the information stored in a volatile semiconductor memory during the loss of electric power.
Typically, these prior art uninterruptible power supplies have a number of disadvantages. In certain devices, the clutch or differential is a weak mechanical link in the system and from time to time requires replacement. Generally speaking, the internal combustion engine, clutch, flywheel, a generator, and A.C. motor must be mounted end-to-end with their respective shafts coupled together. This creates a power supply of considerable physical length which can be difficult to install in a small area. Auxiliary controls must be provided to start the internal combustion engine, to bring it up to speed, and to engage the generator at the proper time. Many of the prior art devices do not operate as load isolators from the power line during normal operations. As a result, fluctuations in electrical power, such as brownouts, would continue to affect the external load.
In order to overcome these problems associated with the prior art, the present inventor developed uninterruptible power systems that are the subject of several patents. For example, U.S. Pat. No. 4,460,834, issued on Jul. 17, 1984 to the present inventor, describes an uninterruptible power system for providing an uninterruptible power supply to an external load. The power system includes a flywheel generator, a first motor, a standby generator, and a transfer controller. The flywheel generator is adapted to supply power to the external load. The first motor is drivingly connected to the flywheel generator. The first motor is adapted to be connected to a source of power external to the power system. The standby generator is electrically connected to the first motor. A standby motor is drivingly connected to the standby generator. The transfer controller is adapted to switchably interconnect the first motor to the source of power and to interconnect the standby generator to the first motor.
U.S. Pat. No. 4,686,375, issued on Aug. 11, 1987 also to the present inventor, shows an uninterruptible power supply co-generation system which includes a first generator connected to a primary external load, a second generator connected to a secondary external load, and a prime mover connected to the first and second generators by a common shaft. The first generator is electrically isolated from the secondary external load. The prime mover is an internal combustion engine that supplies rotational movement to the common shaft. The secondary external load is the electrical utility. A thermal recovery system is connected to the internal combustion engine.
U.S. Pat. No. 8,227,938, issued on Jul. 24, 2012 also to the present inventor, discloses a batteryless starter for an uninterruptible power system. This uninterruptible power systems includes a motor generator means for conditioning electric power, a backup generator means having an internal combustion engine having an electrically-driven starter so as to provide backup electric power, an electrical switch that is electrically connected to power mains and to the electrical output of the backup generator and to the electrical input of the motor generator for selectively switching power from the electric means and the backup generator to the motor generator. The starter switch is electrically connected to the output of the motor generator and electrically connected to the input of the starter system for switchably connecting the output of the motor generator to the starter.
A variety of other patents have also issued relating to such uninterruptible power systems that address certain problems found in the prior art. For example, U.S. Pat. No. 5,053,635, issued on Oct. 1, 1991 to G. West, provides an uninterruptible power supply with a variable speed drive which drives a synchronous motor/generator. The synchronous motor/generator and the variable speed drive are connected to inductively accelerate the motor/generator to near synchronous speed. When the motor/generator assembly reaches near synchronous speed, the motor/generator is switched to synchronous operation, while still under control of the variable speed drive. The variable speed drive is connected to maintain synchronicity with the motor/generator during acceleration.
U.S. Pat. No. 5,646,458, issued on Jul. 8, 1997 to Bowyer et al., provides an uninterruptible power supply that provides conditioned AC power to a critical load. This uninterruptible power system includes a variable speed drive that operates in response to AC utility power or to a standby DC input by providing a motor drive signal. The uninterruptible power supply power conditioning unit further includes a motor-generator that operates in response to the motor drive output by providing the conditioned AC power to the critical load. In response to an outage in the utility AC power, standby DC power is provided by a standby DC power source that includes a variable speed drive and a flywheel motor-generator connected to the variable speed drive. Both the power conditioning unit and the standby DC power source are initially operated in response to the utility AC power. The flywheel motor-generator stores kinetic energy in a rotating flywheel. When an outage occurs, the rotating flywheel continues to operate the flywheel motor-generator of the standby DC power source so as to cause the production of AC power which is rectified and provided as standby DC power to operate the variable speed drive of the power conditioning unit until either the utility AC power outage is over or a standby emergency generator is brought on line.
U.S. Pat. No. 5,767,591, issued on Jun. 16, 1998 to J. F. Pinkerton, discloses a method and apparatus for providing startup power to a genset-backed uninterruptible power supply. In this apparatus, the flywheel energy storage device produces three-phase AC voltage and is used to provide temporary power to a critical load while a backup power supply, such as a diesel generator set is accelerated to full speed. The startup power for the genset is also provided from the flywheel energy storage device through a circuit that converts the AC voltage at one level to DC voltage at a lower level.
U.S. Pat. No. 5,811,960, issued on Sep. 22, 1998 to Van Sickle et al., teaches a batteryless uninterruptible power supply. This power supply converts mechanical rotation generated by a local power source to electrical power in the event of commercial line power distortion or failure. The uninterruptible power supply uses a voltage and frequency-tolerant rectifier-inverter combination that converts the decaying output of a de-accelerating synchronous alternating current machine to a stable alternating current voltage for driving a critical load.
A problem associated with these prior art mechanisms is the amount of delay involved in bringing the internal combustion engine up to a synchronous speed for the production of power. In most circumstances where an internal combustion engine is used or, in particular, a diesel engine is used, a starter is required in order to charge a flywheel to begin the operation of the engine. The starter is typically powered by DC power. As such, there is a small delay (of approximately four to six seconds) in achieving full power production from the engine. As such, a need has developed so as to provide a system whereby the internal combustion engine can be accelerated more quickly and brought up to synchronous speed in a rapid manner.
Starters are somewhat notorious for unreliable operation. As such, whenever the ability to start the internal combustion engine is dependent upon a starter, users of the uninterruptible power supply system are often concerned that if there were a failure of the starter, the backup generator would not be effective in maintaining the uninterruptible load. As such, a redundant system is felt to be desirable so as to assure that internal combustion engine is always operable, even in the event of starter failure.
It is an object of the present invention to provide an uninterruptible power supply system that can be reliably started.
It is another object of the present invention to provide an uninterruptible power supply system that enhances the acceleration of the internal combustion engine for the generation of backup power.
It is another object of the present invention to provide an uninterruptible power supply system that avoids the use of batteries.
It is still another object of the present invention to provide an uninterruptible power supply system that minimizes the amount of control technology required for the operation of the system.
It is a further object of the present invention to provide an uninterruptible power supply system that effectively avoids voltage drops during the startup of the standby generator.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.